This application claims the benefit of Korean Application No. P2000-41369 filed Jul. 19, 2000, which is hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a semiconductor device, and more particularly, to a semiconductor device and a method for fabricating the same which improve the characteristic of stand-by current of an SRAM cell.
2. Background of the Related Art
A related art semiconductor device and method for fabricating the same will be described with the accompanying drawings.
FIG. 1 is a cross-sectional view showing a related art semiconductor device, and FIGS. 2A to 2D are cross-sectional views showing fabricating process steps of the related art semiconductor device. In the drawings, left sides are cross-sectional views of a transistor formed in a peripheral area of an SRAM while right sides are cross-sectional views of a transistor formed in a cell area of the SRAM.
As shown in FIG. 1, a cell area and a peripheral area of the SRAM are defined in a semiconductor substrate 101. A gate electrode 103 is formed on the semiconductor substrate 101, and a gate oxide film 102 is interposed between the semiconductor 101 and the gate electrode 103. In both the cell area and the peripheral area, heavily doped source/drain regions 106 are formed in the semiconductor substrate 101 at predetermined depths with the same distance from the gate electrode 103. Subsequently, lightly doped source/drain regions 110 are formed in the semiconductor substrate 101 between the gate electrode 103 and the heavily doped source/drain regions 106 at predetermined depths.
The lightly doped source/drain regions 110 of the peripheral area and the cell area are formed with the same length as shown in portions A and B of FIG. 1.
Afterwards, a cobalt silicide layer 109 is formed on surfaces of the gate electrode 103 and the heavily doped source/drain regions 106.
Now, a method for fabricating the aforementioned related art semiconductor device will be described with reference to FIGS. 2A to 2D.
The transistor of the cell area and the transistor of the peripheral area are formed at the same time.
As shown in FIG. 2A, the cell area and the peripheral area are defined in the semiconductor substrate 101 and the gate oxide film 102 is formed on the entire surface of the semiconductor substrate 101. Then, a polysilicon layer for gate electrode is deposited on the gate oxide film 102.
Afterwards, the polysilicon layer and the gate oxide film 102 are selectively removed by photolithography and etching processes to form the gate electrode 103 on the semiconductor substrate 101 of the cell area and the peripheral area.
A titanium nitride(TiN) layer is then deposited along the surfaces of the gate electrode 103 and the semiconductor substrate 101 by chemical vapor deposition (CVD). A silicon oxide (SiO2) layer is deposited on the TiN layer.
The silicon oxide layer and the TiN layer are etched back to remain on both sides of the gate oxide film 102 and the gate electrode 103 as well as on the semiconductor substrate 101 adjacent to both sides, so that a nitride film spacer 104 and an insulating spacer 105 are formed thereon.
As shown in FIG. 2B, the insulating spacer 105 is removed, and then heavily doped impurity ions are injected into the entire surface of the semiconductor substrate 101 using the nitride film spacer 104 as a mask, so that the heavily doped source/drain regions 106 are formed in the semiconductor substrate 101 at both sides of the gate electrode 103 and the nitride film spacer 104 at predetermined depths.
As shown in FIG. 2C, a cobalt layer 107 and a TiN layer 108 are sequentially deposited on the entire surface of the semiconductor substrate 101 including the gate electrode 103. At this time, instead of Co of the cobalt layer 107, any one of refractory metals such as W, Ti and Mo may be used.
As shown in FIG. 2D, a cobalt silicide layer 109 is formed on the surfaces of the heavily doped source/drain regions 106 and the gate electrode 103 by a rapid thermal annealing (RTA) process. The cobalt silicide layer 109 includes a cobalt silicide which is a material obtained by reacting silicon of the heavily doped source/drain regions 106 and the gate electrode 103 with cobalt of the cobalt layer 107.
Afterwards, the TiN layer and the cobalt layer 107 which remain without reacting with silicon are removed and then a secondary RTA process is performed for stabilization of the cobalt silicide layer 109.
The nitride film spacer 104 is then removed. Subsequently, as shown in portions A and B of FIG. 2D, the lightly doped source/drain regions 110 having the same length in the peripheral area and the cell area are formed in the semiconductor substrate 101 in which the cobalt silicide layer 109 is not formed, at both sides of the gate electrode 103 by injecting lightly doped impurity ions using the cobalt silicide layer 109 as a mask. Thus, the related art semiconductor device is completed.
However, the related art semiconductor device and method for fabricating the same the following problems.
Since the distance between the gate electrode and the heavily doped source/drain regions formed in the cell area is equal to the distance between the gate electrode and the heavily doped source drain regions formed in the peripheral area, it is difficult to reduce lateral field of the transistor of the cell area. This results in leakage of stand-by current such as gate induced drain leakage (GIDL) when the SRAM cell is not operating.
An object of the invention is to solve at least the above problems and/or disadvantages and to provide at least the advantages described hereinafter.
Another object of the present invention is to provide a semiconductor device and a method for fabricating the same that substantially obviate one or more of the problems due to limitations and disadvantages of the related art.
Another object of the present invention is to provide a semiconductor device and a method for fabricating the same which improve characteristic of stand-by current of an SRAM cell.
Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objects and advantages of the invention may be realized and attained as particularly pointed out in the appended claims.
To achieve at least these objects and other advantages in a whole or in part and in accordance with purposes of the present invention, as embodied and broadly described, a semiconductor device according to the present invention comprises a semiconductor substrate in which a peripheral area and a cell area are defined, a first and second gate insulating layers on the semiconductor substrate of the peripheral area and the cell area, first and second gate electrodes on the first and second gate insulating layers, respectively, first and second heavily doped source/drain regions in the semiconductor-substrate at both sides of the first gate electrode and the second gate electrode, respectively, first and second lightly doped source/drain regions in the semiconductor substrate, adjacent to the first heavily doped source/drain regions and the second heavily doped source/drain regions, respectively, wherein the first and second lightly doped source/drain regions have a different length, and a silicide layer on the first and second gate electrodes and in the first and second heavily doped source/drain regions.
In another aspect, a method for fabricating a semiconductor device according to the present invention comprises the steps of defining a peripheral area and a cell area in a semiconductor substrate to form a first and second gate electrodes in the peripheral area and the cell area, respectively, forming a first insulating spacer having a first length on both sides of the first gate electrode and on the semiconductor substrate, forming a second insulating spacer having a second length longer than the first length on both sides of the second gate electrode, forming first and second heavily doped source/drain regions in the semiconductor substrate at both sides of the first and second insulating spacers, forming a silicide layer on surfaces of the first and second heavily doped source/drain regions and the first and second gate electrodes, removing the first and second insulating spacers, and forming lightly doped source/drain regions in the semiconductor substrate corresponding to a portion where the first and second insulating spacers are removed.
In another aspect of the invention, a method for fabricating a semiconductor device comprises the steps of defining a peripheral area and a cell area in a semiconductor substrate, forming a first gate electrode and a second gate electrode on the cell area and the peripheral area, respectively, forming a first and a second insulating spacers over the first gate electrode and the second gate electrode, respectively, partially removing the first and the second insulating spacers so that the first insulating spacer has a first length, and the second insulating spacer has a second length longer than the length of the first insulating spacer, forming first and second heavily doped source/drain regions in the semiconductor substrate at both sides of the first and second insulating spacers, forming a silicide layer on surfaces of the first and second heavily doped source/drain regions and the first and second gate electrodes, removing the first and second insulating spacers, and forming lightly doped source/drain regions in the semiconductor substrate corresponding to a portion where the first and second insulating spacers are removed.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.